The present invention relates to an electrical flow control valve used in devices such as exhaust gas re-circulation control devices for the purpose of reducing exhaust gas emissions of NOx or the like from internal combustion engines.
FIG. 1 is a block diagram which shows conventional exhaust gas re-circulation control device. In FIG. 1, reference numeral 1 denotes an internal combustion engine, 2 is an intake pipe allowing inflow of air to the engine, 3 is an intake manifold allowing inflow of air to each pipe branching from the intake pipe 2, 4 is an air cleaner provided upstream of the intake pipe 2, 5 is an injector which is provided in the intake pipe 2 and injects fuel. Air entering the intake pipe 2 through the air cleaner 4 flows into the engine 1 together with fuel supplied from the injector 5.
6 represents a throttle valve which varies the degree of air intake into the engine 1 and 7 is an idle rotation speed control valve provided in a bypass which bypasses the throttle valve 6. The gas mixture which enters the engine 1 is ignited by an ignition plug not shown in the figure. After combustion, the exhaust gases pass through the exhaust gas pipe 8, are purified by the purification device 9 comprising a catalytic converter and are expelled into the atmosphere. 10 is an electrical flow control valve of a step motor type which is disposed in the exhaust gas re-circulation passage and controls the flow of exhaust gases in the passage.
11 is an electronic control unit which generates control signals to the electrical flow control valve 10 on the basis of information received from the driving state detection means comprising elements such as a throttle aperture sensor 12 which detects the degree of aperture of the throttle valve 6, a pressure sensor 13 which detects the pressure in the intake pipe, a water temperature sensor 14 which detects the temperature of the engine cooling water, and the ignition device made up of the ignition coil 15 and the igniter 16.
FIG. 2 is a diagram which shows the above electrical flow control valve 10. 21 is a valve housing having an inlet port 21a which communicates with the engine exhaust gas pipe 8, an outlet port 21b which communicates with the engine intake pipe 2 and a rotary flow passage 21c which is the passage between the inlet port 21a and the outlet port 21b. 22 is a valve seat provided in the rotary flow passage 21c of the valve housing 21. 23 is a valve body which opens and closes the aperture of the valve seat 22. 24 is a valve shaft on one end of which the valve body 23 is mounted and which displaces the valve body 23 to the open and closed position by reciprocating motion as a valve rod. 25 is a bush which acts as a bearing for the valve shaft 24 mounted in the valve housing 21. 27 is a spring holder mounted on the other end of the valve shaft 24 which projects externally from the valve housing 21.
28 is a bracket, for example made of cast iron, formed as a unit with the valve housing 21 on the side from which the valve shaft 24 projects from the valve housing 21. The bracket 28 is in a cup shape of fixed height in the shape of a truncated cylindrical concavity on the step motor side (hereafter called the indented part).
A flange element 28b which mounts the stepping motor 29 with a spacing member 31 and a mounting screw 32 through the holder 30 is formed on the stepping motor 29 side of the bracket 28. The cross sectional size of the flange 28b is of a size having the minimum necessary strength to support the stepping motor 29 or is of a slightly larger size (for example a size having a surface area twice that of the necessary strength).
Furthermore around the flange element 28b, an aperture 28c is formed which communicates with the indented part 28a. Then on the valve housing side 21 of the bracket 28, a holder 26 is formed which prevents the build-up of deposits within the vertical range of the bush 25 displaced by the valve shaft 24.
The motor holder 30 is made of material having good thermal conductivity, a lower bearing 33 is mounted in the central lower hollow part, and the length of an integrated heat radiating fin 35 forms a gap 34 between the valve housing on the valve housing side. These components make it possible to decrease the transmission of high temperature exhaust gases to the step motor 29.
Next, the components of the step motor 29 will be explained. 36 is a hollow motor housing, 37 is a rotor which is supported in free rotation by a ball 49 and a sleeve bearing 38 at its upper end, and by a lower bearing 33 at its lower end. A magnet 39 is mounted on its outer periphery. The central part of the rotor 37 is hollow in the vertical direction, displaces vertically and has a threaded section 37a formed on its inner face.
40a and 40b are upper and lower yokes which are mounted on the inner part of the motor housing 36 so as to face the magnet 39 of the rotor 37 and in the inner part of which are housed bobbins 41a and 41b. 42a1 and 42a2 are coils wound around the bobbin 41a, 42b1 and 42b2 are coils wound around the bobbin 41b, and 43 is a plate magnetically separating the upper and lower yokes 40a and 40b. 44 is a protective plate which is provided in the upper part of the motor housing 36 for preventing entry of resinous material into the insertion part of the rotor when forming the motor housing 36. 45 is an actuator rod which is supported in a threadedly engaged state by the threaded section 37a of the inner part of the rotor 37 and which projects downwardly from the motor holder 30. The tip of the actuator rod 45 displaces vertically and pushes against the valve shaft 24.
Due to the fact that the actuator rod 45 is prevented from rotating by the bearing of the actuator rod and the motor bush 54 which has a rotation prevention function, the actuator rod 45 displaces vertically in response to the rotations of the rotor 37. A stopper 45b is provided in the actuator rod which pushes against and detaches from the stopper 37b of the rotor 37 and limits the upward displacement above a fixed amount. 46 is a plate which is assembled in the indented part 37c which is provided on the upper end of the rotor 37. 47 is an indented part which is formed on the protective plate 44 on the shaft line of the rotor 37, and which centers the ball 49 on the plate 46.
50 is a SPL washer for providing pre-load to the lower bearing 33. 51 is a connector which supplies electrical pulses to each coil. As shown in FIG. 4, the connector 51 comprises the terminals{circle around (1)}-{circle around (6)} which are electrically connected to the coils 42a1, 42a2, 42b1, 42b2, and the connector housing 51a. As shown in FIG. 3, switching transistors Tr1-Tr4 are connected to the ground line of the terminals, {circle around (1)}, {circle around (3)}, {circle around (4)}, {circle around (6)}. Terminal {circle around (2)} to which one end of the coils 42a1 and 42a2 is connected and terminal 5 to which one end of the coils 42b1 and 42b2 is connected, are connected to the electrical supply terminal +B through the switch SW. The connector housing 51a and the motor housing 36 are integrated by resinous material. 52 is a coil spring which intercalates between the spring holder 27 and the bracket 28. The coil spring pushes the valve shaft 24 upwardly towards the middle of the figure through the spring holder 27 and maintains the valve body 23 in a closed state. While in a closed state, a gap is formed between the valve shaft 24 and the actuator rod 45 and the valve body 23 is maintained in an accurately closed state.
Next the operation of the electrical flow control valve will be explained. The rotor 37 of the stepping motor 29 which acts as a motive source does not rotate continuously but only makes a single rotation. If an electrical current is applied to the top of the coils 42a1 and 42a2 in a counter-clockwise direction as viewed from above, the upper face of the coils will be a north pole N, the lower face will be a south pole S and the stator will be a north pole. Likewise if a current is applied to the lower face of the coils 42b1 and 42b2, a magnetic pole will be generated in the stator. As a magnet is provided which is minutely divided into S poles and N poles in the rotor, the rotor 37 rotates to a stabilized position in the stator. As shown in FIG. 4 one step at a time is rotated by changing the phase in a sequential manner. For, example when the valve body 23 is in the opened position, the phase is changed in the sequence 0xe2x86x921xe2x86x922xe2x86x923xe2x86x920xe2x86x921, when in the closed position the phase is changed in the sequence 0 xe2x86x923xe2x86x922xe2x86x921xe2x86x920xe2x86x923. In response to the rotations of the rotor 37, the actuator rod 45 which threadedly engages with the threaded section 37a of the rotor 37 moves downwardly in the figure, repelled by the elastic force of the coil spring 52 which is compressed between the bracket 28 and the spring holder 27, displaces the motor shaft 24 downwardly and opens the valve body 23. In such a way, the flow of the high temperature engine exhaust gases on the inlet port side 21a of the valve housing 21 is controlled by the valve body 23 and is directed to the outlet port side 21b through the rotary flow passage 21c. 
Furthermore since generated poles of the stator rotate in the opposite direction if the conducting phase order with respect to the coils 42a1, 42a2, 42b1, 42b2 is changed, the rotor 37 is rotated in the opposite direction to the above. In response to the direction of rotation of the rotor 37, the actuator rod 45 displaces upwardly towards the middle of the figure. As a result, the valve shaft 24 displaces upwardly towards the middle of the figure due to the coil spring 52 and the valve 23 closes. When the stopper 45b reaches the stopper 37b of the rotor 37, the displacement of the actuator rod 45 terminates.
Since the conventional electrical flow control valve is constructed as above, the centering of the rotor 37 is carried out by the sleeve bearing 38 and the indented part 47 of the protective plate 44 which receives the ball 49 which is provided between the motor housing 36 the plate 46 which is provided on the end face of the rotor 37 and the sleeve bearing 38. Thus, the conventional electric flow control valve creates the problems of too many parts, difficulty of assembling and higher costs because the sleeve bearing is expensive.
There is the further problem that the positional accuracy (degree of coaxiality) of the motor housing and the boss of the motor holder needs to be, increased since the boss of the motor holder performs the positional determination of the bearing which receives the other end of the motor shaft.
The present invention is proposed to solve the above problems. It has the object of dispensing with the spring bearing and reducing the number of parts and the cost. It has the further object of easily increasing the positional accuracy of the bearing.
The present invention relates to an electrical flow control valve which displaces an actuator rod by reciprocal motion by the action of a motor, which impels a valve shaft normally biased in the direction of valve closure and opens a valve. A retention section is provided which has the function of centering a ball which should be maintained between one end of a rotor and the opposing face of that end. As a result it is possible to dispense with a sleeve bearing. Hence, friction can be reduced, as well as costs.
The axial alignment accuracy of the motor housing is simply improved by the provision of a boss which projects from a motor housing towards a motor holder, which is integrated with a motor housing and which retains a bearing in a fixed position.
A retention section is provided which has the function of centering a ball which should be maintained between one end of a rotor and the opposing face of that end. A boss is provided which projects from a motor housing towards a motor holder, which is integrated with a motor housing and which retains a bearing in a fixed position. Thus, it is possible to dispense with a sleeve bearing and to simply improve the axial alignment accuracy of the motor and the stator.